Background: Our ability to predict respiratory compromise during general anesthesia in a child with an anterior mediastinal mass is limited. Two prior reports have found a correlation between adequacy of ventilation during general anesthesia and the tracheal cross-sectional area obtained from computed tomograms (computed tomography [CT] scans). These and other reports have suggested that pulmonary function tests may provide additional information regarding anesthetic risks, but no studies have evaluated the extent of respiratory compromise in children with an anterior mediastinal mass.
Methods: We prospectively evaluated 31 children with mediastinal masses before 34 surgical procedures. At each evaluation the tracheal area (as a percent of the predicted area on the basis of age and gender) was determined by CT. Pulmonary function tests were performed in the sitting and supine positions. The eleven children with either a tracheal area or peak expiratory flow rate (PEFR) of less than 50% of predicted received only a local anesthetic; the majority of children above these levels (17 of 22) received a general anesthetic.
Results: Eleven of 31 patients had significant pulmonary restriction as defined by total lung capacity of less than 75% of predicted. Eight patients had a PEFR in the supine position of less than 50% of predicted. PEFR was lower in the supine than the upright position in all patients (median value of decrease, 12%). In 28 of 34 evaluations the child had a tracheal area greater than 50% of predicted, a criterion proposed for safe utilization of general anesthesia. This latter guideline, however, did not identify all patients with significant impairment of pulmonary function; five patients had a PEFR of less than 50% of predicted but tracheal areas of greater than 50% of predicted. All children were administered anesthetics uneventfully with these guidelines.
Conclusions: Although the tracheal area can be accurately measured with the CT scan, this does not identify all children with mediastinal masses and abnormal pulmonary function. A large mass may produce significant restrictive impairment and hence reduction in PEFR by the intrathoracic volume it occupies and yet not cause tracheal compression. It may also reduce the PEFR by narrowing the bronchi distal to the carina. Currently no CT standards exist for measuring bronchial areas in children. Our study did not evaluate whether impaired pulmonary function as measured by PEFR would be predictive of respiratory collapse during general anesthesia because all were excluded and operated on under local anesthesia. General anesthesia was well tolerated in children with tracheal area and PEFR greater than 50% of predicted. Pulmonary function tests in children with anterior mediastinal masses may add valuable information to the anatomic evaluation obtained by CT scan.